Internal combustion engines are used in a variety of environments. In the case of a working machine provided with an internal combustion engine, for example, the working machine may produce dust during working operation. Air cleaners for internal combustion engines (hereinafter referred to as internal combustion engine air cleaners) are required to be capable of constantly supplying sufficiently-filtered air to the internal combustion engine via a carburetor even though they are used in a variety of environments. Thus, improvement in internal combustion engine air cleaners has been under way in recent years, examples of which are disclosed in Japanese Utility Model Application Post-Exam Publication No. HEI-05-33727 (hereinafter referred to as “Patent Literature 1”) and Japanese Patent Application Post-Exam Publication No. HEI-02-39286 (hereinafter referred to as “Patent Literature 2”).
In the internal combustion engine air cleaner disclosed in Patent Literature 1, an air outlet port is formed in a bottom plate of a case accommodating therein an annular filter element, and air filtered through the filter element is supplied to the carburetor via the air outlet port. The air outlet port is surrounded by the filter element and also covered with a cylindrical filter provided in an inner space defined by the annular filter element.
In the internal combustion engine air cleaner disclosed in Patent Literature 2, an air outlet port is formed in a bottom plate of a case accommodating therein a generally cylindrical filter element, and air filtered through the filter element is supplied to the internal combustion engine via the air outlet port. The air outlet port is surrounded by the filter element, and a support frame section extends upward from an upper surface portion of the bottom plate around the air outlet port. The filter element is placed on the support frame section, then a cover is placed on the bottom plate, and then the filter element and cover are bolted together to the upper surface of the support frame section. In this manner, the filter element and cover are fixedly mounted on the bottom plate of the case via the support frame section.
Generally, if used for a long time, the air cleaner filter element would be clogged with various dust, such as dust in the air. Thus, there arises a need to inspect and clean or replace the filter element at suitable time intervals. As the filter element is detached from the case, dust adhering to the filter element can fall onto the bottom plate of case. In cleaning the dust accumulated on the bottom plate, a human operator has to pay close attention to avoid the dust entering the air outlet port. Thus, the cleaning of the air cleaner tends to be cumbersome and troublesome operation.